1. Field of the Invention
The present invention relates to a sealing technique of a cylindrical alkaline dry cell.
2. Description of the Background Art
<Entire Schematic Structure of a Cylindrical Alkaline Dry Cell>
For example, as illustrated in FIG. 15, a conventional cylindrical alkaline dry cell (dry battery) is provided with: a cathode 2 and an anode 4, a separator 3 placed between these electrodes, a nail-shaped anode collector rod 5 inserted into the anode 4 and an electrolyte solution (not shown) in which the separator 3 and the cathode 2 are impregnated, all of which are housed inside (cell chamber C) an external can 1 that has a cylindrical shape with a bottom lid and that also serves as a cathode terminal, and an opening edge 1a of the external can 1 is sealed so as to prevent the electrolyte solution inside the cell chamber C from leaking outside.
<A Thickness of External Can>
The outer diameter of a size “AA” alkaline dry cell that is one type of cylindrical alkaline dry cells is determined to 13.5 to 14.5 mm in the Japanese Industrial Standards (JIS standards), and the size of the battery holder in apparatuses using the battery is unified in such a manner that in fact, the outer diameter is standardized to 14.0±0.1 mm. In an attempt to increase the discharging capacity by increasing the inner volume (cell volume) of an alkaline dry cell with the outer diameter being limited, the can thickness of the external can is decreased. However, in the case when the thickness of the external can made of a killed steel (aluminum killed steel) that is generally used in alkaline dry cell is reduced, problems tend to arise in which a difficult machining process is required and the external can tends to be deformed during a transporting process of the external can or a transferring process at the time of assembling the battery. For this reason, even the thinnest can thickness of the external can of the size “AA” alkaline dry cell that are currently available in the domestic market is set to 0.18 mm.
<Structure of Sealing Member>
As illustrated in FIG. 16 in an enlarged manner, the sealing member in the cylindrical alkaline dry cell is provided with a resin sealing member 6 having a safety valve mechanism for preventing an abnormal rise of the inner pressure, that is, for preventing explosion, a supporting member 107 for supporting the resin sealing member 6 with the inner circumferential portion and an anode terminal plate (anode terminal) 207 formed in an upward sticking manner (hat shape) in the Figure. Among these members, the resin sealing member 6 is provided with a boss section 61 for holding the anode collector rod 5, an outer circumferential portion 62 that is made in contact with the inner circumferential face of the external can 1, and a connecting portion 63 for connecting the boss section 61 and the outer circumferential section 62 with an anti-explosion thin portion (actuating point of the safety valve) 63a being placed on one portion thereof. Here, in the case when the inner pressure of the battery, that is, the pressure inside the cell chamber C, exceeds a predetermined level, the connecting section 63 is deformed in a swelling manner, for example, as indicated by a chain line in the Figure, and when the inner pressure further increases, the anti-explosion thin portion 63a is ruptured (that is, the safety valve is actuated) as illustrated in FIG. 17, with the result that the inner pressure is released outside. Moreover, the resin sealing member 6 prevents the electrolyte solution from leaking by blocking the upper portion of the cell chamber C, as well as electrically insulating between the external can 1 forming the cathode collector and the anode terminal plate 207 forming the anode collector terminal. Here, in FIG. 16 and FIG. 17, reference numerals 107f and 207f respectively show gas releasing holes for externally releasing gas generated inside the cell chamber C.
In the resin sealing member 6 of this type, the outer circumferential portion 62 thereof, located between the supporting member 107 and the external can 1, is tightened inward together with the circumferential edge of the opening edge 1a of the external can 1, and then caulked so that it is attached inside the opening edge 1a of the external can 1 (in this specification, such a sealing method is referred to as “sealing process by lateral tightening” or “lateral tightening sealing process”). In this case, in the case when the caulking force is weak, even though the electrolyte solution (a strong alkaline solution mainly composed of potassium hydroxide) inside the battery is not allowed to leak for the initial time, as the closely contacting property between the sealing member 6 and the external can 1 reduces due to the succeeding temperature changes, etc., the electrolyte solution inside the battery gradually leaks outside through the border portion between the sealing member 6 and the external can 1. For this reason, in the conventional cylindrical alkaline dry cell, a metal washer (a disc-shaped metal plate having a hole in the center) having a predetermined thickness (in general, approximately 0.6 to 0.75 mm) is used as the supporting member 107 that supports the sealing member 6 with the inner circumferential side, with the result that, upon tightening the outer circumferential section 62 of the sealing member 6, the metal washer is used for firmly backing up the tightening process from the inside thereof so that the outer circumferential section 62 of the sealing member 6 can be caulked with a sufficient force from outside together with the opening edge la of the external can 1.
<Subject 1 (Common Subject)>
In the above-mentioned cylindrical alkaline dry cell, one proposed method for increasing the charging capacity is to increase the inner volume of the battery. The respective inventions of the present application have a common objective for increasing the charging capacity by increasing the battery inner volume, and with this objective as the premise, attempts are made to solve the subjects described below.
<Subject 2>
First, the inventors, etc. of the present invention tried to use a thin external can having a thickness of not more than 0.18 mm so as to increase the charging capacity by increasing the inner volume in a size “AA” alkaline dry cell that is one type of cylindrical alkaline dry cell. Consequently, various revising means are given so that, with respect to the difficulty in forming the external can and the problem of deformation at the time of transportation that have been described, it becomes possible to solve these problems. However, in the case when the thickness of the external can is set to be thinner than 0.18 mm, since the caulking strength of the sealing member is reduced, a new problem arises in which the inner electrolyte solution leaks from the sealing portion. Upon assembling a battery, the sealing member 6 to which the anode collector rod 5, the anode terminal plate 207, etc. have been assembled, is inserted into the opening edge 1a of the external can 1, and in this state, the outer circumferential portion 62 of the sealing member 6 is tightened by the external can 1 from the outer circumferential side as well as by the metal washer (metal plate) 107 with the inner circumferential side, and then caulked so that it is attached to the inside of the opening edge 1a of the external can 1. In this case, the sealing member is deformed so that the outer circumferential portion 62 of the sealing member 6 is pressed onto the inner face of the external can 1 by its elastic force, and allowed to closely contact it. Consequently, gaps caused by fine irregularities located on the surface (contact face to the external can 1) of the outer circumferential portion 62 of the sealing member 6 are filled so that it is possible to prevent a strong alkaline solution (electrolyte solution) with a strong creeping property, stored inside the battery, from leaking outside.
However, in the case when a thin external can having a thickness of not more than 18 mm, since the strength of the external can 1 decreases to an extent corresponding to the reduced thickness, the external can 1 fails to suppress the deformation of the resin sealing member, with the result that the electrolyte solution inside the battery comes to leak outside through the fine irregularities between the resin sealing member. In particular, when the battery is subjected to an abrupt temperature change, the leak of the electrolyte solution tends to occur due to the swell and shrinkage of the material. In the anti-leakage solution test carried out by the present inventors, etc., more specifically, tests in which a battery has been stored in a thermostat that repeats temperature changes between −10° C. and 60° C. every 30 minutes for three days, and this is then observed as to the presence or absence of leak from the sealing portion, it has been recognized that the solution leakage occurs when the thickness of the external can is set to not more than 0.18, and this problem has not been solved by the conventional method.
In the present invention, even in the case when an external can having a thickness of not more than 0.18 mm is used so as to increase the charging capacity, it is possible to prevent the electrolyte solution inside the battery from leaking outside even upon application of an abrupt temperature change thereon. This is one of the objectives of the present invention.
<Subject 3>
Next, in order to increase the inner volume of the battery, the inventors, etc. of the present application have taken a close look at the thickness of the sealing member. Here, in the cylinder-type alkaline dry cell, since the structure in which the center portion of the anode terminal plate 207, that is, the portion of the terminal face, is shaped into a protruding form has been the standard structure, the conventional sealing structure, shown in FIG. 15 and FIG. 16, that has a metal washer as the supporting member 107 for supporting the outer circumferential portion 62 of the sealing member 6 (hereinafter, reference numeral 107 is also used as the metal washer, if necessary) comes to have two upper and lower void portions in the height direction with the metal washer 107 interpolated in between, that is, a space S1 on the connecting section 63 side of the sealing member 6 and a space S2 on the anode terminal plate 207 side. Of these, the former space S1 is a necessary portion for allowing the deformation of the connecting portion 63 of the sealing member 6 or its thin portion 63a resulting from an increase in the inner pressure; however, the latter space S2 is formed because of the fact that the anode terminal plate 207 has a protruding shape toward the surface side, and is a wasteful portion that can be eliminated originally. Since such a wasteful space S2 is located on the sealing member, the conventional sealing structure tends to have an unnecessary thickness of the sealing portion as a whole, resulting in a problem of a limited volume of the cell chamber C to be filled with a battery activating substance directly related to the charging capacity, that is, a limited inner volume of the battery.
Here, in order to prevent the volume of the sealing portion from becoming unnecessarily large, a possible proposal is to eliminate the metal washer 107 and to utilize the anode terminal plate 207 instead as the supporting member for supporting the sealing member 6 from the inside portion. However, from the viewpoint of manufacturing costs, a member that is thinner than the metal washer 107 (normally, one having a thickness of 0.4 mm) is used as the anode terminal plate 207; therefore, when the above-mentioned method is adopted, the anode terminal plate 207 is deformed upon caulking the sealing member 6, resulting in an insufficient force for tightening the outer circumferential portion 62 of the sealing member 6. For this reason, upon application of an abrupt temperature change, etc., to the battery, the inner electrolyte solution might leak outside through the gap between the external can 1 and the sealing member 6.
In the present invention, in the cylindrical alkaline dry cell having the resin sealing member, only one sheet of a metal plate that also serves as the anode terminal plate (anode terminal) is used as the supporting member supporting the sealing member with the inner circumferential portion, and the shape of the outer circumferential portion of this is also devised; thus, it is possible to prevent the thickness or the volume of the sealing portion from becoming unnecessarily large, and also to prevent the electrolyte solution inside the battery from leaking outside even in the event of a temperature change, etc. This arrangement is also one objective of the present invention.
<Subject 4>
Moreover, in the case when only the anode terminal plate is used as the supporting member for supporting the sealing member 6 with the inner portion, after the sealing portion has been formed by the caulking process, deviations tend to occur in the height of the anode terminal plate. This phenomenon of height deviations will be discussed below in detail. Here, as will be described later, a bent portion (curved portion) having an angle greater than 90 degrees with an average curvature radius of not more than 1 mm is placed on the outer circumferential portion of the anode terminal plate as will be described later, the caulking portion is desirably formed through a process curing, thereby making it possible to prevent the inner strong alkaline electrolyte solution from leaking outside; therefore, the following description will be given by exemplifying the case in which the anode terminal plate having the curved portion on the outer circumferential portion.
FIG. 11 shows one example of such an anode terminal plate. The anode terminal plate 307, shown in the Figure, is provided with three areas including a terminal face 377 that comes into contact with the terminal of a battery applied apparatus to supply power thereto, a side face 379 of this terminal face 377 and a flange face 378. In the case when the curved portion is placed on the outer circumferential portion of the anode terminal plate 307, the flange face 378 is classified into a portion having been subjected to the curving process (a curved portion 378b) and a comparatively flat portion (a flange face flat portion) 378a. 
In the process for sealing the opening of an alkaline dry cell, the external can is plastically deformed by caulking so as to tighten the resin sealing member sandwiched between the anode terminal plate 307 and the external can, and at this time, a stress component toward the radial direction is applied onto the anode terminal plate 307. This stress causes the anode terminal plate 307 to deform; however, this deformation takes place at a crossing point serving as a starting point between a face that is in parallel with the stress and a face having an angle close to 90 degrees with respect to the stress, and in FIG. 11, the deformation takes place with point A (a crossing point between the terminal face 377 and the side face 379 of the terminal face) and point B (a crossing point between the terminal face side face 377 and the flange face flat portion 378a) serving as fulcrums. The deformation causes point B to become higher than the original position, or causes point B to become lower than it, resulting in a difference in height in the anode terminal plate 307 between the two cases. As to whether the height of the anode terminal plate 307 becomes higher or lower than the height before the caulking process, it depends on a slight difference of conditions of the sealing process, and is consequently instable with chaotic variations.
Deviations in the height of the battery cause problems. For example, if there is a deviation in height on one battery is 0.5 mm, the maximum deviation of an apparatus housing six batteries in series with each other is 3 mm in the total length of the battery heights, with the result that the collector function of the apparatus is not properly exerted or the apparatus might fail to properly house the batteries. For this reason, for example, in the case of the size “AA” alkaline dry cell that are commercially available in the domestic market, the height of the batteries is set within the range of 50.00 mm±0.05 mm.
In the present invention, in the case when an anode terminal plate is used as the supporting member for supporting the resin sealing member with the inner circumference portion in the alkaline dry cell having the resin sealing member, deviations in dimension due to the deformation in the anode terminal plate in the sealing process is reduced as small as possible. This is one of the objectives of the present invention.
<Subject 5>
As described earlier, upon assembling an alkaline dry cell, the resin sealing member 6 to which an anode collector rod 5, an anode terminal plate 207, etc. have been assembled is inserted into the opening edge 1a of the external can 1, and in this state, the outer circumferential portion 62 of the sealing member 6 is tightened by the external can 1 from the outer circumferential portion, and is also tightened by the metal washer (metal plate) 107 with the inner circumferential portion, and then caulked so that it is attached inside the opening edge 1a of the external can 1. At this time, the resin sealing member is deformed, and the outer circumferential portion 62 of the sealing member 6 is pressed onto the inner face of the external can 1, and closely made in contact therewith.
However, in the conventional sealing construction in which the thickness of the connecting portion 63 is comparatively thin, and its portion on the outer circumferential section 62 and its portion on the boss section 61 side do not have so much a difference in the thickness, the sealing member 6 or its connecting section 63 is greatly deformed as a whole at the time of the sealing process by the lateral tightening operation, resulting in an excessive load on the anti-explosion thin portion (the actuation point of the safety valve) 63a in the connecting section 63, that is, a problem of too much stress on the corresponding thin portion 63a. 
In the present invention, during such a lateral tightening operation at the time of the sealing process, the stress exerted on the anti-explosion thin portion is reduced so that it is possible to improve the reliability of the thin portion functioning as the safety valve. This is also one objective of the present invention.
<Subject 6>
In the alkaline dry cell provided with the resin sealing member 6, when the safety valve is operated properly, the inner gas is externally released through the gas releasing holes 107f and 207f placed in the metal washer 107 and the anode terminal plate 207. In the safety valve, the connecting portion to the sealing member 6 is deflected upward by an increase in the inner pressure of the battery, and when the inner pressure exceeds a predetermined pressure, the anti-explosion thin portion 63a formed in the connecting portion 63 is ruptured so that it is actuated.
However, in the conventional sealing member structure, the thickness of the connecting portion 63 is comparatively thin, and there is not so much difference in thickness between the portion on the outer circumferential 62 side and the portion on the boss section 61 side; therefore, for example, in the event of a short-circuiting heat generation, the resin of the sealing member comes to soften, allowing the connecting section 63 to extend before the actuation of the safety valve to block the gas releasing hole 107a of the metal washer 107, or in the case when the anode terminal plate 207 is used as the metal washer in the supporting member, allowing it to contact the anode terminal plate 207 to prevent the inner gas from being smoothly released. Moreover, in the event of an excessive discharging state, the safety valve fails to function properly, causing the sealing member 6 to rupture with the contents scattering with a big rupturing noise.